Row crop sowing machines or seed planters for single seed sowing have been widely used for decades. Usually, said machines comprise at least one rotating disc for holding and supplying the seeds to be planted and means for releasing and conducting the seeds to the furrows on the ground at determined depths and spacing.
The rotating discs usually comprise holes, pockets, cradles or teeth for retaining the seeds with the help of vacuum or positive air pressure that is interrupted at a desired point in order to let the seeds drop into conducting means to the ground.
Most known sowing machines comprising a plurality of metering discs rely on only one driving assembly for simultaneously rotating all discs. In case of machines comprising a large number of metering discs, e.g. 20 or more, said driving assembly is bulky, complicated and expensive, not allowing the individual adjustment of the rotation of each metering disc, necessary in occasions when the sowing machine is not supposed to follow a rectilinear path, wherein the more external sowing devices run for a longer distance than the more internal ones.
Such drawbacks were addressed by the use of hydraulic systems for driving individually each disc, comprising sophisticated electronic control means, requiring both expensive and continuous maintenance.
Some late developments in sowing machines, replaced said hydraulic systems by individual electric motors, leading to much simpler and economic equipment, as particularly disclosed in patent application WO 2012/142607 A1 where the motors are connected to the axles of the metering discs.
Nevertheless, there is still a need for simpler metering devices, with reduced power requirements, and less expensive building and maintenance.